<!DOCTYPE html>
<html>
<head lang="en">
    <meta charset="UTF-8">
    <title></title>

    <style>
        p {
            /* The following line prevents the text from being enlarged */
            /*-webkit-text-size-adjust: 100%;*/
        }
    </style>
</head>
<body>

<p id="line1" style="font-size: 15px;">This is a line of text inside a frame.</p>
<p style="font-size: 15px;">This is another line of text inside a frame.</p>

<script>
    var element = document.getElementById("line1");
    var styles = getComputedStyle(element);
    alert(styles.getPropertyValue("font-size"));
</script>

</body>
</html>